Metal detectors and gold, etc.

If metal detectors detect metal by flux in magnetic fields, as I assume, how do they detect non-ferrous metals like gold and silver with any accuracy?

I just thought that it’s setting up a current in the lost treasure, and the current is running into the ground, causing a higher energy output from the battery, which of course can be detected. Is that right?

Dave, you’re confusing the phenomenon of ferromagnetism (the alignment of microfields produced by electron spins into a macrofield that is statically impressed on a lump of iron) with that of electromagnetism in general.
Take a length of silver wire (this may remain a Gedankenexperiment if you can’t afford it), may a coil out of it, hook it up to a non-constant electric source, and check the magnetic flux (for a purely quantitative measurement, a decent compass will do). You’ll see that there is a magnetic field.

“Kings die, and leave their crowns to their sons. Shmuel HaKatan took all the treasures in the world, and went away.”

Well, I’m not sure how Akatsukami’s experiment relates to the metal detector exactly, but. . . The metal detector has, I believe, a couple of fairly high-frequency oscillators which beat to produce an audio tone. One of the oscillators has a detector coil which can couple some of its energy to any conductor in the ground. If a current is coupled into such a conductor via the detector coil, the oscillator it’s in the circuit of becomes slightly detuned, thus causing the beat tone to change its resultant audable pitch in the instrument’s earphones.


Gold? Like say, rings? ANyway those are usually 14k & that means they aren’t pure gold but a metal mix which the detector picks up. Sterling silver also is not pure silver.

Metal detectors pick up things which are a) good conductors or b) ferromagnetic. Materials like copper, aluminum, gold, silver are not ferromagnetic, but conduct electricity well. It’s not necessary for them to be alloyed with other materials in order to detect them with a metal detector.

It’s relatively difficult for detectors to pick up non-magnetic stainless steel because it isn’t magnetic (obviously) and it doesn’t conduct electricity particularly well either.